1. Technical Field
The present disclosure relates to a method for making thermoacoustic elements.
2. Description of Related Art
Acoustic devices generally include a signal device and a sound wave generator. The signal device inputs signals to the sound wave generator such as a loudspeaker. Thermoacoustic effect is a conversion between heat and acoustic signals. The thermoacoustic effect is distinct from the mechanism of the conventional loudspeaker, which makes sounds by using the pressure waves created by the mechanical movement of the diaphragm. When signals are inputted into a thermoacoustic element, heat is produced in the thermoacoustic element according to the variations of the signal and/or signal strength. The produced heat is propagated into surrounding medium. The heating of the surrounding medium causes thermal expansion of the surrounding medium, thus producing pressure waves in the surrounding medium, and resulting in sound wave generation. Such an acoustic effect induced by temperature changes is commonly called the “thermoacoustic effect”.
A thermophone based on the thermoacoustic effect was created by H. D. Arnold and I. B. Crandall (H. D. Arnold and I. B. Crandall, “The thermophone as a precision source of sound”, Phys. Rev. 10, pp 22-38 (1917)). They used platinum strip with a thickness of 7×10−5 cm as a thermoacoustic element. The heat capacity per unit area of the platinum strip with the thickness of 7×10−5 cm is 2×10−4 J/cm2·K. However, the sound made by the thermophone adopting the platinum strip is extremely weak because the heat capacity per unit area of the platinum strip is too high.
Graphene is a carbonaceous material composed of carbon atoms densely packed in a two dimensional honeycomb crystal lattice. The graphene has excellent electrical and thermal properties. An electron mobility of the graphene at room temperature is greater than 15000 cm2V−1s−1. A thermal conductivity of the graphene is greater than 3000 Wm−1K−1. The graphene has been applied in different fields such as field emission or sensor. However, the graphene is rarely applied in the thermoacoustic element.
What is needed, therefore, is to provide a method for making a graphene based thermoacoustic element having an improved sound intensity.